Canadian Consulting Engineer

2021 #CCEawards Showcase: Hot Pipeline Condition Assessment Study

“The acoustic monitoring technique they used to assess the wall of the pipes was ingenious. They adapted geophysics to something that’s not in the ground, which is quite unusual.”- Jury

October 31, 2021  By CCE

Hot pipeline study

Photos courtesy CIMA+.

Category: Buildings

Award of Excellence Winner: CIMA+

The Greater Toronto Airports Authority (GTAA) owns and operates hot-water closed-loop pipeline network, with carbon steel pipes operating at high temperatures to ensure continuity for Toronto Pearson International Airport. The GTAA engaged CIMA+ to develop a conditional assessment for these pipelines, based on its own inspection standards, and thus avoid unnecessary shutdowns and/or using invasive tools.

Based on the findings of CIMA+’s study, this year the GTAA has completed an inspection of the entire population of hot-water pipes at Canada’s largest airport, while they are in service and fully operational.

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Environmental significance

Hot water systems convey not only water, but also chemicals designed to allow the water to run at high temperatures and to provide a corrosion barrier for the internal surface of the pipeline.

The water is in a closed-loop pipe system; any drainage is conducted within that system, using storage in boilers. So, any unexpected failures and main breaks would lead to hot water spills that could present a health and safety hazard, due to high temperatures and the chemicals that could reach major watercourses and/or combined sewer systems around the airport.

The spilled water could eventually reach treatment plants and cause significant issues to the treatment process, due to the highly concentrated chemicals in the water.

Hot pipeline inspection

GTAA needed a way to inspect the entire population of hot-water pipes at Canada’s largest airport, while they are in service and fully operational.

A novel approach to acoustics

GTAA needed to develop an assessment method for challenging pipeline systems where the carrier is inside a conduct, given the limitations and constraints resulting from system operating conditions (i.e. high temperatures) and their limited tolerance for inspection risks, with preference given to external, non-invasive tools.

Acoustics is a well-known technology for inspecting potable watermains and buried pipelines, but it is limited to those installed in a compacted backfill, not in a void like GTAA’s hot pipeline setup. When an acoustic stress wave is introduced on a pipe’s external wall surface (i.e. by tapping with a rubber hammer on the external surface), it will vibrate at a macroscopic level, causing radial displacements that affect the sound wave velocity inside the hot water body. When a pipe is not compacted in backfill, the boundary conditions for equilibrium are not the pipe wall, but rather the void surrounding the carrier pipe.

To address this issue, CIMA+ chose to introduce the acoustic sound wave in two forms simultaneously. The first form introduces the sound wave outside the pipe, similar to regular acoustic technology, but using a constant frequency of tapping on the pipe’s external wall surface. The second form uses a high-amplitude sonar wave to measure deformations from inside the pipe.

With these two waves, acoustic measurements can be compared to a point where the frequencies correlate, providing a conclusive result for wave velocity. Once the velocity is determined, the pipe’s remaining wall thickness can also be calculated, using a transient wave velocity formula.

This concept enabled the use of modified acoustic technology to assess the hot-water pipes while they were in-service, with no operational changes. And when the system is offline in the summer, GTAA can address repairs and replacement needs identified during an assessment that was conducted at the beginning of the year. Indeed, the study allowed the client to develop a seasonal maintenance cycle of assessment and renewal (as needed) during each year, increasing the reliability of its hot water pipeline system.

Watercourses and sewer access

It is important to prevent spills that could reach nearby watercourses and sewers.

A multi-stage plan

The project presented two major challenges: (a) securing funds to conduct a trial and validation of the proposed idea and (b) turning the idea of constant external noise into reality by building a sensor.

To address these challenges, CIMA+ developed a multi-stage plan. The first step included a presentation of the proposed acoustic modification, supported by simulation modelling and a detailed budget, to get GTAA’s buy-in.

Once that budget was approved, the second step was to engage an acoustic technology vendor to design and build the equipment. The proposed solution was a ‘shaker’ sensor that would vibrate at a wide range of frequencies that could correlate with sonar waves introduced inside the pipes.

The third stage included choosing a ‘testbed’ pipe and performing actual field measurements, using the newly developed tools. Once results were provided with a range of accuracy, the fourth and last step was to validate the results and their accuracy by collecting a sample of the inspected pipe and conducting pit depth measurements at a third-party specialized lab.

The results came back with an average of 6% accuracy, exceeding the original expectation of 10%—and this could be increased by assessing the air inside the pipe, since trapped air inside a water body impacts the wave velocity being measured.

 

Hot Pipeline Condition Assessment Study, Mississauga, Ont.

Award-winning firm (prime consultant): CIMA+, Mississauga, Ont. (Rabia Mady, P.Eng.).

Owner: Greater Toronto Airports Authority (GTAA).

Other key players: Kenaidan Contracting.


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